Abstract
May I congratulate Lewis Clark on his paper covering the analysis and planning of step drawdown tests. I think the subject of well performance is due for a ‘shake-up’ and this paper will hopefully initiate some useful scientific discussion in the right direction. I have two main criticisms to make. The first one is that the author considers only continuous step drawdown tests; he makes no mention of conducting discontinuous or intermittent step drawdown tests in which each drawdown step is followed by a recovery period of at least equal duration. I have used both types of test and have found the latter provides the more reliable results for the following reasons: (i) the problem of errors caused by fluctuations in pumping rate within a given step affecting the reliability of data from subsequent steps does not arise; (ii) the problem of errors caused by extrapolating the time-drawdown trend in order to calculate incremental drawdown does not arise; (iii) the analysis of transmissivity from the time-drawdown data is straightforward; each drawdown step is treated simply as a short constant rate test, and since errors caused by (i) and (ii) will not exist, the values thus obtained will be more reliable; (iv) there will be as many recovery steps to analyse as there are drawdown steps, and hence more ‘stabs’ at transmissivity. The recovery ‘ Q ’ values are the same as the preceding drawdown step value; the problem of estimating an averaged or weighted effective ‘ Q ’ for the recovery test does not
Published Version
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